PURPOSE: To enhance the toughness of a molded product and to eliminate residual voids and to enhance the limit of accuracy by a method wherein a glass base composite material is heated to be molded in a pellet shape and the molded pellets are preheated to specific temp. to be supplied into a heating cylinder and further heated to be injected in a molten state.

CONSTITUTION: The pellets 41 composed of a glass base composite material received in a hopper 40 are held to the temp. range from the transition point of a glass material to the softening point thereof and heated and melted within a heating cylinder 1 while rotated by a screw 33 to be supplied to a storage part 43. When the storage part 43 is filled with the glass base composite material, the rotation of the screw 33 is stopped and the glass base composite material of an injection molding shot is cooled in a cavity 30 and, after the completion of cooling, mold opening is performed to eject a molded product by an ejector and mold clamping is again performed to start injection. That is, at the time of injection, the screw 33 is advanced to the foremost injection position by an injection cylinder.